Patellofemoral pain (PFP) syndrome is one of the most common abnormalities involving the knee. Current literature suggests a multifactorial etiology and it is commonly accepted that abnormal patellar tracking, patellar malalignment, and quadriceps imbalance are closely related to PFP. The purpose of the proposed research is to determine whether imbalances in the soft tissue structures surrounding the knee contribute to PFP by inducing pain secondary to patellar malalignment and maltracking. A noninvasive system for in vivo measurement of patellar movement in six degrees-of-freedom will be designed and validated. Development of quantitative diagnostic tools for PFP could lead to better characterization of PFP syndrome, allowing treatment methods to be tailored to individual needs and leading to improved functional outcomes. The diagnostic system will then be used to quantify patellar maltracking in PFP subjects. Finally, we will attempt to elucidate the nature of the quadriceps imbalance which leads to patellar maltracking in PFP. A thorough understanding of the etiology of PFP will highlight future research directions for this syndrome. We propose to develop a more cohesive picture of the underlying neuromechanical mechanisms of PFP syndrome; such that we may evaluate the pathological changes associated with PFP accurately, and improve functional outcomes due to more effective treatment methods for PFP syndrome.